This invention relates to a method and apparatus for fastening together frame elements, such as the frame elements of a picture frame.
In the production of frames of the type used to mount pictures or mirrors and similar objects, and in the production of panel doors for kitchen cabinets and of the frames for the door openings, the elongated frame elements usually are formed with end surfaces oriented at angles with respect to the longitudinal axis of the frame elements with the grain of the wood extending along the length of each frame element and the angled end surfaces of a frame element is matched together with a similar angled end surface of an adjacent frame element to form a mitered joint, and the frame elements are connected together by a fastener. In most instances the mitered joints will be 90.degree. joints that form the frame elements in a rectangular shape; however, other angles and shapes can be formed.
One process used for fastening mitered joints is to insert at least one nail into the outer edge surface of one frame element through that frame element, through the mitered joint, and into the adjacent frame element. As the fastener is driven through the mitered joint, the force applied to the fastener and to the frame elements tends to compress or draw together the mitered joint. A second fastener can then be driven from the edge surface of the adjacent frame element through the mitered joint, and this usually forms a firm connection between the frame elements. Some disadvantages of this type connection procedure are that the head portions of the fasteners are visible at the edge of the frame when the frame is hung on a wall, or if the fasteners are counter sunk into the frame elements the holes or the putty covering the holes are visible, a multiple number of fasteners are required for each joint to form a stable frame, there is a hazard that the fasteners will hit each other as they are driven into the frame, and if the frame is held in a jig and fasteners are driven simultaneously through both of the frame elements at the corner of the frame, two fastener tools are required for the process.
Another process for joining frame elements together in a mitered joint is to place the angled end surfaces of the frame elements together to form the mitered joint and then to insert a staple or similar fastener into the back surfaces of the frame elements at a right angle with respect to the surfaces of the frame elements so that the fastener straddles and therefore connects together the frame elements. Since the movement of the fastener into the surfaces of the frame elements usually does not tend to draw the frame elements together, the firmness of the connection between the frame elements depends upon the operator's technique, and if the operator is not diligent in pressing the frame elements together during the fastening procedure, a loose joint is formed.
Another process for joining frame elements together in a mitered joint is to form a kerf in each frame element adjacent the mitered joint on the unexposed surfaces of the joint, with the kerfs extending parallel to the angled end surfaces of the frame elements and then inserting a clamp into the kerts. A disadvantage of this process is that it requires additional labor and time, and therefore is expensive.
A recently developed apparatus functions to hold the angled frame elements together to form an abutting mitered joint and to insert a fastener to the joint from the back surface of the frame at an angle sloped toward the inside of the frame. The fastener is shaped so that it tends to draw the joint together as it enters the frame material. The sharpness of the fasteners and the force and direction in which the fasteners are to be inserted into the frame elements require safety features to be included in the apparatus so as to avoid injury to the operator of the apparatus.